Which coordinate system to use? Job spans multiple

Hi all,

I'm stumped on setting up a proper geodatabase structure for a large utility job. I have features in multiple coordinate systems so I've split them into multiple feature classes. This is causing me all kinds of problems in my Add-ins. I'd like to project the points all in UTM I guess, but the data is being collected in different state plane coordinate systems. I don't know how to handle bringing it all into one feature class and projecting the points in UTM in a single mxd. I haven't found a guide of any kind for working with this kind of data. Is this a simple operation, or does it require hefty setup and maintainance?

Not sure this is the correct forum for this topic. I'll repost elsewhere if this is the wrong place.

Thanks in advance,
cdebruin